Apparatus and method for operating internal combustion engines from variable mixtures of gaseous fuels

ABSTRACT

An apparatus and method for utilizing any arbitrary mixture ratio of multiple fuel gases having differing combustion characteristics, such as natural gas and hydrogen gas, within an internal combustion engine. The gaseous fuel composition ratio is first sensed, such as by thermal conductivity, infrared signature, sound propagation speed, or equivalent mixture differentiation mechanisms and combinations thereof which are utilized as input(s) to a “multiple map” engine control module which modulates selected operating parameters of the engine, such as fuel injection and ignition timing, in response to the proportions of fuel gases available so that the engine operates correctly and at high efficiency irrespective of the gas mixture ratio being utilized. As a result, an engine configured according to the teachings of the present invention may be fueled from at least two different fuel sources without admixing constraints.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. provisional applicationserial No. 60/225,017 filed on Aug. 11, 2000, incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.DE-FC36-94G010039 awarded by the U.S. Department of Energy. TheGovernment has certain rights in this invention.

REFERENCE TO A COMPUTER PROGRAM APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains generally to internal combustion enginesutilizing gaseous fuels, and more particularly to a method and apparatusfor operating an internal combustion engine at high efficiency from anarbitrary mixture of multiple gaseous fuels such as hydrogen and naturalgas.

2. Description of the Background Art

The current use of fossil fuels, such as gasoline, diesel fuel, andnatural gas, to power various forms of internal combustion engines, inparticular those incorporated within motor vehicles, has a number ofserious shortcomings in view of dwindling fossil fuel resources and theincreasing awareness of the detrimental effects of pollution. The desireto enjoy abundant energy while striving for the benefits of clean airhave led to the consideration of various alternative energy sources forpowering equipment such as motor vehicles. The use of renewable forms ofenergy is highly preferred to assure that energy remains abundantdespite dwindling fossil fuel resources.

In recent years, the desire to use clean, renewable, vehicle energysources has been evidenced by a push toward the use of electricalvehicles. The adoption of electrical vehicles, however, has proceededslowly and a number of electric vehicle manufacturers have discontinuedsales. Despite the enormous expenditures to develop electric vehiclesand recharging equipment, the fundamental shortcomings of the technologyand infrastructure have never been overcome. It should be appreciatedthat, although electrical energy may be readily converted to mechanicalenergy without generating high emission levels, electrical energystorage within batteries has many inherent drawbacks, including the timerequired to recharge a battery, the cost of batteries, and the weightper unit of energy stored within a battery. In contrast, conventionalinternal combustion engines (ICE) powered from liquid or gaseous fuelsmay be readily “recharged” by refueling, while the fuels themselvesprovide about a thirty-fold increase in energy storage density whencompared with battery energy sources. However, the drawbacks associatedwith emissions and other environmental concerns, as well as thenon-renewable nature of these fossil fuels, remain.

In response to these concerns, a number of alternative fuels have beenconsidered to reduce air-borne emissions while maintaining theconvenience and energy storage efficiency that are inherent within acombustion process. Increasingly, attention is being focused on hydrogenas a fuel for use within both internal combustion engines (ICE) and fuelcells. When utilized within an ICE, it should be appreciated thathydrogen provides a clean burning renewable energy source that may bereadily produced. Home hydrogen refueling appliances have been proposedfor use with hydrogen vehicles which are small in size and capable ofgenerating sufficient hydrogen to power a vehicle for a trip spanning afew hundred miles. Vehicles incorporating hydrogen powered internalcombustion engines have been studied and have been found to providesignificant benefits from lowered emission levels and fuel renewability.

On-board vehicle energy reforming is also being considered, wherein ahydrogen powered vehicle is provided with a fuel reformer that convertsthe available fossil fuel to hydrogen gas which is utilized to operate ahydrogen combustion engine or a hydrogen fuel cell. A number ofdisadvantages exist, however, with regard to the adoption of on-boardreforming for the purposes of facilitating the introduction of vehicleswhich operate from hydrogen fuel cells.

The adoption of hydrogen as an energy source has been a slow process,perhaps due in part to the inherent difficulty of changing an existinginfrastructure to accommodate the use of hydrogen. The presentinfrastructure is lacking in both vehicles and fueling facilities thatare capable of using, or distributing, hydrogen. Changing the presentinfrastructure to provide hydrogen distribution while synchronouslydeveloping and deploying hydrogen-fueled vehicles is a formidablechallenge. It will be appreciated that vehicle manufacturers areresistant to invest in the development and marketing of hydrogenvehicles until the fuels are readily available, while fuel manufacturersare resistant to invest in widespread hydrogen production anddistribution facilities until vehicles exist for consuming hydrogenfuels.

On the other hand, natural gas is a widely distributed form of gaseoushydrocarbon fossil fuel that typically comprises methane, althoughproportions of ethane, propane, and butane may also he present.Presently, an infrastructure exists to distribute natural gas for use inmany applications, including motor vehicles. It should be appreciatedthat, at one point in recent history, automobiles and fuel distributionfacilities were being rapidly adapted for the use and distribution,respectively, of natural gas because the prices of natural gas were wellbelow that of gasoline and the conversion process was inexpensive. Thetransition from natural gas to hydrogen gas may appear trivial in thatvehicles configured for burning natural gas may be reconfigured toexclusively burn hydrogen gas. One key difference between these fuels,however, is the energy density contained per cubic foot. Natural gasprovides a significantly higher energy density than hydrogen gas, andconsequently, an engine configured to operate on hydrogen gas, insteadof natural gas, requires a higher fuel volume per combustion cycle todeliver a given rated horsepower and torque. Therefore, it will beappreciated that combustion variables must be reconfigured to providefor the burning of hydrogen gas. Consequently, the adoption of hydrogengas as a “replacement” for natural gas would not solve the inherentinfrastructure problems associated with the introduction of a newincompatible fuel source, and the conversion of vehicles to hydrogencould only be expected after an adequate hydrogen fuel distributionnetwork had been established.

The use of hydrogen as an energy source within internal combustionvehicles has additional aspects that should be appreciated. First,although the hydrogen combustion process involves burning increasedvolumes of gaseous fuel, the resulting emissions contain lower levels ofair pollutants and carbon dioxide than a comparable engine generating agive horsepower when operating from a natural gas fuel source. Second,hydrogen is a renewable fuel source that may be generated from a numberof low-cost processes, whereas natural gas is a limited fossil fuelresource. It is anticipated, therefore, that the cost of fossil fuelswill increase as the supply dwindles and that the low cost of generatingrenewable hydrogen will become increasingly attractive. The widespreaduse of hydrogen in future vehicles should then result in a lower costper mile than that obtainable through the use of non-renewable fossilfuel resources.

Despite the inherent emission and renewability advantages of hydrogenuse, the implementation of hydrogen vehicles has proceeded slowly. Itwill be appreciated that convenient operation of a hydrogen vehicle overdistances requiring refueling has not been possible thus far due to alack of hydrogen fuel distribution facilities. Experimental hydrogenvehicles are therefore only capable of operating within a limitedcommute radius about a facility-based refueling station.

The deployment of a substantial number of vehicles capable of operatingfrom hydrogen would be an impetus for establishing the necessaryelements of a hydrogen-fueling infrastructure. An internal combustionengines fueled by pure hydrogen would be capable of operating over alarge range of fuel-air mixture ranges, including operation at afuel-air mixture that is as lean as one fourth of stoichiometric fuel.It will be appreciated that in order for the hydrogen to he completelyconsumed a specific volume of air is required. The combustion process isgenerally given by the following formula:2H₂+(O₂+3.77N₂)=>2H₂O+3.77N₂  (1)As a result of the combustion process, a total of 4.77 volumes of airare required for every 2 volumes of hydrogen utilized in the combustionprocess. This ratio is commonly referred to as a stoichiometric massratio of 34.3:1.

Optimal efficiency with a hydrogen ICE is attained at equivalence ratioφ of about 0.4, whereas a natural gas engine typically operates slightlylean of stoichiometric. By way of reference, it will be appreciated thatthe equivalence ratio is defined as the fuel/air mixture rationormalized by the stoichiometric fuel/air mass. Efficiency is extremelyimportant for hydrogen fueled vehicles, as the available fuel storagevolume limits vehicle range. The hybrid electric configuration istherefore attractive for hydrogen fueled vehicles due to the ability toset up the engine to operate at substantially constant speed at peakefficiency consistent with low emissive output. Furthermore, the flamespeed of a hydrogen-air mixture is substantially above that of a mixtureof natural gas and air, although the speeds are decreased as themixtures are made more lean. Fixed mixtures of hydrogen and natural gashave been developed, most notably Hythane™ which is a mixture of naturalgas containing about 15% hydrogen, wherein the hydrogen contributesapproximately 5% energy of the combustion energy. The Florida SolarEnergy Center has experimented with mixtures having fixed percentages ofhydrogen and methane. These mixtures utilize specific ratios of hydrogenup to about 36%, by volume, within the natural gas to contribute up toapproximately 12% of the gaseous fuel energy. Researchers noted that theaddition of hydrogen to natural gas aids lean operation and cleanburning, and that either pure hydrogen or 30% hydrogen/natural gas canfuel an ICE so as to meet the EZEV (Equivalent Zero Emissions Vehicle)standard.

This body of work on the use of hydrogen fuel, and fuels containinghydrogen, indicates that efficient combustion may occur with naturalgas, hydrogen, or a specific mixture thereof. However, because the fuelmetering and timing of a vehicle is determined by the fuel beingutilized, these fuels require that the engine be designed orspecifically configured for use with a chosen fuel mixture. This imposessignificant limits on the fuel mixtures that can be employed.

Therefore, a need exists for equipment and methods to ease thetransition from conventional fossil based fuels to the widespreadadoption of hydrogen fuel. The present invention satisfies that need, aswell as others, and overcomes the deficiencies of previously developedvehicle energy solutions.

BRIEF SUMMARY OF THE INVENTION

The present invention generally comprises a method and apparatus foroperating an internal combustion engine from any arbitrary mixture ofgaseous fuels. More particularly, the present invention comprises avariable gaseous fuels (VGF) engine which is capable of operating from afuel source containing an arbitrary mixture of natural gas and hydrogengas. Note that in the present invention the mixture can vary as opposedto being fixed. Accordingly, the terms “variable gaseous fuels” and“VGF” as used herein should not be confused with the use of conventionalmixed fuels having a fixed mixture ratio or “composition”, such as “FlexFuel” which comprises a fixed ratio of gasoline and methanol, or“Hythane™” which comprises a fixed ratio of hydrogen and natural gas.

By way of example, and not of limitation, the VGF engine of the presentinvention determines the ratio of the available gases mixed within, orbeing received from, the vehicle's fuel storage tank and modulates theparameters of the combustion process accordingly to provide efficientcombustion for any arbitrary mixture of gases. It will be appreciatedthat the admixed gaseous fuels for operating the VGF engine may bereceived from a single pressurized fuel tank, or from any alternativemechanism capable of supplying a mixture of hydrogen and natural gas.

A VGF engine according to the invention is preferably configured forburning any arbitrary mixture of natural gas and hydrogen. In operation,the VGF engine measures the relative mixtures of the two gases in thefuel supply, such as within the fuel storage tank or in the fuelconnections that lead from the fuel tank to the engine, and adjustscombustion parameters accordingly. The amount of fuel being metered intothe engine is then modulated in response to the measured ratio of gaseswithin the mixture and the associated energy densities thereof.

The invention includes means for determining the gaseous fuelcomposition so that combustion parameters may be adjusted, such as fuelvolume and ignition timing, to assure efficient operation for any givenmixture of gaseous fuel. In gaseous mixtures of hydrogen and naturalgas, for example, the fuel flow rate must be increased as the ratio ofhydrogen gas to natural gas is increased due to the lower energy densityof the hydrogen gas. Accordingly, a VGF engine according to the presentinvention preferably includes fuel composition sensors that are capableof measuring the gaseous fuel composition, as well as an electronicengine control module (ECM) that scales the amount of fuel being meteredinto the combustion chamber and that optionally modifies additionalcombustion parameters such as ignition timing, valve timing, and soforth. By measuring the gaseous mixture ratio within the fuel storagetank or in the fuel connections that lead from the fuel tank to theengine, the control electronics can compensate for the fuel mixturebefore any improperly adjusted combustion cycles can occur.

It will be appreciated that the gaseous fuel composition sensor may heimplemented in a number of ways that allow the mixture ratio of thecomposite gases to be determined. Although the term fuel compositionsensor is utilized herein, the sensor could alternatively be referred toas a fuel mixture ratio sensor, and so forth, without departing from thepresent invention.

A number of forms of internal combustion engines, such as conventionalpiston engines, rotary engines, sterling engines, and so forth, arecapable of being separately configured to operate from fuels havingdifferent combustion properties and may he adapted for operation from avariable gaseous mixture of fuels according to the teachings of thepresent invention. It will be appreciated that sensing gaseous fuelcomposition and adjusting combustion variables accordingly are functionsthat may be readily incorporated within modern internal combustionengines, since modern engines are being increasingly designed towardfull electronic control of all aspects of the combustion process, suchas fuel metering, ignition timing, valve operation, and so forth.

The gaseous fuel composition (mixture ratio) may be determined in anumber of ways by analyzing one or more differentiable characteristicsof the gaseous fuel supply prior to combustion, or by analyzingcombustion results, or by combinations thereof. For example,characteristics which may be utilized to differentiate hydrogen gas fromnatural gas include thermal conductivity, infrared signature, soundvelocity, and so forth. One or more of these characteristics may bedetected using sensors and the resultant data used to determine themixture ratio. It should be appreciated that the characteristics of thegas which are measured for determining a gaseous mixture ratio wouldpreferably be substantially immune to changes in temperature, pressure,water vapor, selected additives, and similar non-mixture relatedcharacteristics, or would allow non-mixture related variables to beeliminated by electronic or computational means.

For example, measuring the thermal conductivity of a gaseous fuelmixture can be performed with a thermal conductivity sensor whichcommunicates a thermal conductivity signal to a programmed electronicengine control module. The thermal conductivity signal is interpreted bythe ECM to determine a fuel quantity compensation value basedsubstantially on relative energy densities within the constituentcomponents of the gaseous mixture. The ECM then modulates the quantityof gaseous fuel being metered into the combustion chamber in response toits anticipated energy density as based on the fuel compositioninformation received from the fuel composition sensor. It will also beappreciated that a number of internal combustion engines utilize a fuelmetering means, such as fuel injectors which meter fuel to the cylindersin response to the pulse-width of a received gas metering signal.

The ECM therefore meters an appropriate volume of gaseous fuel into eachcylinder in response to the composition of the available gaseous fuel,along with traditional fuel metering determinants such as throttlesetting, RPM, temperature, and the like. Incorporating gaseous fuelcomposition sensing and the ability to adjust fuel metering and otheroptional combustion parameters in response to fuel composition resultsin a VGF engine according to the present invention which is capable ofbeing efficiently operated from a source of gaseous fuel which containsany proportion of natural gas and hydrogen.

An object of the invention is to expedite the transition from the use offossil fuels to a renewable hydrogen energy source by providing anengine capable of operating on any mixture of either fuel source.

Another object of the invention is to provide a variable gaseous fuelengine capable of being utilized within a motor vehicle.

Another object of the invention is to provide an engine capable ofproperly combusting an arbitrary mixture of two gases contained within asingle fuel tank.

Another object of the invention is to provide a method for determiningthe composition of a gaseous mixture of natural gas and hydrogen gas.

Another object of the invention is to provide an electronic enginecontrol module that is capable of responding to the composition of thegas source by modulating combustion parameters such as fuel metering andignition timing.

Further objects and advantages of the invention will be brought out inthe following portions of the specification, wherein the detaileddescription is for the purpose of fully disclosing preferred embodimentsof the invention without placing limitations thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood by reference to thefollowing drawings which are for illustrative purposes only:

FIG. 1 is a functional block diagram of a variable gaseous fuels engineaccording to the present invention.

FIG. 2 is a cross-sectional schematic view of a gas composition sensoraccording to an aspect of the present invention, shown with a heatedfilament being retained within the gas mixture from which the gascomposition may be detected.

FIG. 3 is a schematic diagram of a sensor test bench utilized within thepresent invention for testing aspects of gaseous mixture sensing.

FIG. 4 is a graph showing filament resistance within a gaseous mixturesensor according to an embodiment of the present invention in responseto temperature changes.

FIG. 5 is a graph showing filament resistance at different filamentcurrents when exposed to either hydrogen gas (H₂), or natural gas whichtypically comprises a major percentage of methane gas CH₄.

FIG. 6 is a graph showing sensor resistance within a fixed mixture ratioof hydrogen gas and natural gas in response to temperature and pressurechanges as determined for an embodiment of the composition sensor withinthe present invention.

FIG. 7 is a graph showing sensor voltage in response to gas compositionand pressure changes as determined for an embodiment of the compositionsensor within the present invention.

FIG. 8 is a graph showing gas composition as determined from mixturesensor voltage at selected temperatures as determined for an embodimentof the composition sensor within the present invention.

FIG. 9 is a block diagram of a gaseous mixture sensor according to anaspect of the present invention, shown with a microprocessor forcalculating a gaseous fuel composition (mixture ratio) value from sensormeasurement data.

FIG. 10 is a schematic diagram of an variable gaseous fuels engineconfigured for operation with variable gaseous fuels according to anembodiment of the present invention, showing the modulation of fuelmetering and ignition timing in response to the gaseous fuelcomposition.

DETAILED DESCRIPTION OF THE INVENTION

For illustrative purposes, the present invention is embodied in theapparatus and method generally shown and described herein with referenceto FIG. 1 through FIG. 10. It will be appreciated that the apparatus mayvary as to configuration and as to details of the parts, and that themethod may vary as to the specific steps and sequence, without departingfrom the basic concepts as disclosed herein.

In general terms, the present invention comprises a variable gaseousfuel (VGF) engine that is capable of operating on any mixture ratio of afirst gaseous fuel, such as hydrogen, and a second gaseous fuel, such asnatural gas. It will be appreciated that the invention provides for theoperation of a vehicle, or other gaseous fuel internal combustion enginedevice, from any arbitrary mixture of hydrogen and natural gas, andtherefore creates a bridge to facilitate the transition from dwindlingfossil fuels to a renewable hydrogen energy source.

Vehicles incorporating VGF engines according to the present inventionare capable of utilizing currently available natural gas andtransitioning to hydrogen fuel as sources of supply become more readilyavailable. A VGF engine equipped vehicle according to the presentinvention is capable of operating from any available gaseous source ofeither gas or combined mixture of the two gases. The VGF engine isconfigured for sensing the composition (mixture ratio) of the availablegaseous fuel utilizing an electronic sensor capable of differentiatingone or more characteristics of a first gaseous fuel from a secondgaseous fuel and adjusting combustion parameters accordingly. Importantcombustion parameters to be controlled include fuel quantity andignition timing so that efficient combustion may be achieved regardlessof the specific gas mixture ratio being combusted.

FIG. 1 illustrates the elements of a VGF engine 10 according to thepresent invention which generally comprises an internal combustionengine 12 receiving a mixture of gaseous fuels through a pressureregulator 14 from a gaseous fuel tank 16. Combustion within engine 12 iscontrolled by sensing the gaseous fuel mixture within fuel compositionsensor 18, the information being utilized by an engine control module 20that controls parameters of the combustion process within internalcombustion engine 12. Designing or configuring an engine for VGFoperation according to the present invention requires the addition of afuel composition sensing means and an engine control system capable ofmodulating the gaseous combustion volumes in response to the compositionof the gas being received. It should be appreciated, however, that theadditional sensors and control processing to provide VGF operation areeasily incorporated within modern engines that are typically designedusing electronic control systems which control an increasing number ofcombustion parameters.

Variable gas mixtures may be stored within any gaseous fuel tank 16system capable of storing natural gas. Typically, a pressure regulator14 is utilized on the fuel tank 16 to reduce tank pressure to a constantvalue, typically about 10bar (145 psi), prior to receipt by the gaseousmixture metering system within engine 12. However, it should beappreciated that the need for a pressure regulator, and the pressure towhich such a regulator is adjusted, depends on the fuel metering devicesincorporated within the engine. The metering system of engine 12 isresponsive to the measured mixture ratio of hydrogen gas to natural gas,while additional combustion parameters, such as ignition timing, mayalso be adjusted.

FIG. 2 illustrates a fuel composition sensor 18 capable of determiningthe gaseous mixture ratio (composition) of the available gaseous fuel.Fuel composition sensor 18 is preferably positioned toward an enginefuel intake to determine combustion parameters based on the compositionof incoming variable gaseous fuels.

An example of a sensor suitable for fuel composition sensor 18 is athermal conductivity sensor which is retained in fluidic contact, orsubstantially surrounded by, the available gaseous fuels. One form ofelectronic sensor that may be utilized has been developed by the Collegeof Engineering “Center for Environmental Research and Technology”(CE-CERT) at the University of California, Riverside.

It will be appreciated that hydrogen and natural gas exhibit markedlydissimilar thermal conductivity values, which allows gas composition ofa mixture of hydrogen and natural gas to be readily determined from themeasured thermal conductivity. The composition of a natural gas/hydrogenblend may be readily determined from the output of the thermalconductivity sensor under a set of given conditions. When positionedwithin the gaseous intake of the engine, the thermal conductivity sensoroutputs a signal that is indicative of the mixture ratio of the receivedgaseous fuel at the given temperature and pressure conditions. Thethermal conductivity sensor may therefore be utilized as an input to a“multiple map” engine control module which controls the parameters ofcombustion within the internal combustion engine, such as fuel injectorsand ignition timing. It will be appreciated that additional engineparameters may also be controlled to optimize engine operation for thegiven fuel mixture, such as valve actuation, engine cooling, and soforth.

Fuel composition sensor 18 should be positioned to establish fluidiccontact with the gaseous fuel that will be received by the combustionengine. The sensor preferably comprises a housing 22 configured with oneor more passageways, such as a passageway 24 having an intake end 26 andan output end 28. Preferably fuel mixture sensor 18 is located along thepathway by which the gaseous fuel is conveyed to the combustion chamberof the engine.

By way of example, a section of fuel flow passageway 24 receives amixture of gaseous fuel from a gaseous fuel storage tank 16 withinintake end 26 which is output through output end 28 to pass the gaseousfuel mixture to internal combustion engine 12, wherein it will be routedpast a fuel metering device to one or more combustion chambers. Sensingof the fuel composition is illustrated in a preferred configurationwithin a separate chamber 30 which partially isolates the fuel flowsensor from changes in convective cooling that occur in response tovariations of gas flow rate. A thermal conductivity sensor element,comprising filament 32 with electrical connections 33, is positionedwithin chamber 30.

A quantity of energy is input to the filament so as to heat the filamentto a temperature above that of the gaseous fuel mixture which is influidic contact with the filament. The temperature attained by thefilament within the gaseous fuel mixture is moderated by conductiveenergy losses which depend on the thermal conductivity of thesurrounding gaseous fuel. For example, given any predetermined level offilament heating current, the temperature of the filament when retainedin fluidic contact with hydrogen will be at a lower temperature than thesame filament under identical conditions retained in fluidic contactwith natural gas, due to the higher thermal conductivity of hydrogen gaswhich conducts increased levels of thermal energy away from thefilament. The increased thermal conductivity of the hydrogen gasincreases the amount by which the temperature of the filament ismoderated by the conductive cooling. Given a sufficient differencebetween the thermal conductivity properties of two gases, such as existbetween hydrogen gas and natural gas, the composition of the gaseousfuel may be determined. Energy is supplied to filament 32 by electricalconnections 33 through which current is induced to flow through filament32, while the voltage expressed across the filament as a result of thecurrent flow is substantially indicative of the temperature of thefilament in response to the thermal conduction of the surrounding gas.Stated another way, energy is dissipated from passing a first electricalcurrent of sufficient amperage to heat the filament to a temperaturewhich exceeds the gaseous fuel temperature. The thermal conductivity ofthe gaseous fuel is then determined by analyzing the conductive heatdissipation which occurs, as exhibited by the moderation of filamenttemperature, in response to the thermal conductivity of the gaseous fuelat the elevated filament temperature. It will be appreciated thatincreasing the amount of energy dissipated within the filament, and thusthe amount by which the filament temperature exceeds the gaseous fueltemperature, generally increases the resultant signal which is generatedby the thermal conductivity sensor due to the increased amount ofconductive heat dissipation.

A number of methods exist for determining the temperature of the gaseousfuel proximal to gaseous fuel composition sensor 18, such as byutilizing a temperature sensor or another thermal conductivity sensor.One preferred method of sensing gaseous fuel temperature utilizes thesame thermal conductivity type gaseous fuel composition sensor 18operating in a different sensing mode. It should be appreciated that theresistance of the sensing element, filament 32, within gaseous fuelcomposition sensor 18 changes in response to the amount of electricalcurrent flow and the temperature of filament 32. As a result, thepassage of very small currents through the filament, insufficient tosubstantially alter filament temperature, provides a means fordetermining gaseous fuel temperature. It is only upon substantiallyincreasing filament current to cause sufficient filament heating thatthe thermal conductivity of the surrounding gaseous mixture may bedetermined from the convective losses and the gas fuel compositioncalculated from the thermal conductivity.

While gaseous fuel composition sensor 18 has been described as beingpreferably located within the gaseous fuel intake of the engine, itshould be appreciated that the fuel composition sensor may bealternatively positioned within the gaseous fuel storage tank, or withina device that is in gaseous contact thereof. It should be appreciatedthat positioning the sensor in the fuel intake can provide increasedaccuracy because the fuel mixture ratio that exists within the gaseousfuel lines near the fuel intake of the engine may not changesimultaneously with a change in the mixture ratio of the tank, such asimmediately following refueling of the gaseous fuel tank. Therefore,sensing the fuel mixture ratio at the intake can provide improvedcomposition accuracy as the mixture ratio is sensed just prior tocombustion. It should also be appreciated, however, that an auxiliary,or alternative, fuel mixture ratio measurement system can be performedas a post-combustion fuel ratio measurement. Information received from apost-combustion system would be preferably utilized for performing minoradjustments to the gas flow and engine operation, otherwisecomplications can arise in response to rapid gas mixture ratio changes.

Filament 32 preferably comprises a metallic resistance wire. By way ofexample, a Tungsten filament may be utilized, that preferableincorporates approximately two to ten percent Rhenium. One preferredfilament material is manufactured by GOW-MAC Instrument Company whichcomprises Tungsten having approximately five percent Rhenium. A numberof factors should be considered when selecting the material, gauge, andstructure of the filament, including the temperature, corrosivenessand/or oxidation characteristics of the material to be analyzed. It willbe appreciated that within a flowing environment of hydrogen gas andnatural gas (which typically comprises about 80% methane), the oxidativeimpurity level within the fuel gas and the excitation current levelutilized are important determining factors of sensor longevity. Filament32 is preferably located within a chamber 30 that is retained in fluidcommunication with the passageway through which the gaseous fuel mixtureflows. Chamber 30 is shown configured as a “T-shaped” branched line todesensitize the fuel mixture sensor 18 to the effects of convectiveflow.

EXAMPLE 1

Care should be taken in designing the structure of the fuel sensor asthe internal diameter 34 of the branched line for the sensing elementand the distance between sensor element and fuel flow line 36 have beenfound to be important considerations in providing an adequate sensorsignal level with a sufficiently rapid response time. By way of example,a suitable fuel sensor structure was fabricated with a chamber having adiameter 34 of about one-half centimeter (0.53 cm actual diameter usedin testing) whereas filament 30 was offset 36 from the center of the gasflow passageway by a distance of about two centimeters (2.3 cm actualoffset utilized in testing). It will be appreciated therefore that highsignal levels and low susceptibility to gaseous flow rate were obtainedwith the offset distance being approximately four times (4×) that of thechamber diameter. It should also be appreciated, however, that thefilament may be isolated from the convective flow using alternativemethods known to one of ordinary skill in the art without departing fromthe teachings of the present invention. A constant current source wasutilized for heating the wire, and a digital voltmeter with differentialinput was used to measure the voltage of the filament exposed to thegaseous fuel flow.

It will also be appreciated that inclusion of non-filament voltagedrops, such as those which occur within the wiring connecting thecurrent source to the filament, will reduce the accuracy of filamentvoltage measurement and thereby the accuracy of the computed fuelcomposition. At low current levels the resistance of the filament isindicative of filament temperature which should be largely determined bythe temperature of the gaseous fuel surrounding the filament. Theresistance of the filament may be determined by dividing the measuredfilament voltage by the applied filament current according to theapplication of Ohm's Law, R=V/I. Upon applying a sufficient level ofcurrent to the filament, it begins heating up toward an equilibriumtemperature that is in excess of the surrounding gaseous flow. Theamount of resultant temperature increase for a given heating currentlevel is subject to the thermal conduction of the filament within thesurrounding gaseous fuel composition. The large difference in thermalconductivity between hydrogen gas and natural gas allow the thermalconductivity value for the gaseous fuel mixture to be used todifferentiate the relative composition of the gaseous mixture.Determinations of gaseous fuel composition are preferably performed ascalculations, or table lookups, based on empirically derived equationsor mappings for the given filament structure under the given operatingconditions.

EXAMPLE 2

FIG. 3 illustrates a sensor test bench that was utilized for testinggaseous fuel composition sensor 18 as shown in FIG. 2. Test measurementswere taken with fuel composition sensor 18 positioned within atemperature controlled oven 40. Oven temperature was measured utilizingan integrated circuit temperature sensor, specifically a model LM35 fromNational Semiconductor Incorporated®. The temperature sensor wasutilized to control the temperature in conjunction with a personalcomputer to provide feedback for any desired value from ambienttemperature to about 350 degrees Kelvin. Two kinds of calibration wereperformed with sources of pure methane 42 or pure hydrogen 44 that couldbe fed into fuel composition sensor 18 simultaneously, or sequentially,with the operation of a solenoid valve. The desired gas flow rate wasadjusted by a needle valve and a ball flow meter 46, 48 for a range offlow situations from a static, no flow condition, to about two litersper minute. A calibration measurement of the resulting actual flow ratewas observed from the motion of a soap bubble meniscus in a burette andgas pressure was adjusted with pressure regulators 50, 52, and thepressure value was sensed by pressure transducer 54, such as a BournsIncorporated® model ST3100 pressure transducer capable of registeringpressure from zero to two hundred pounds per square inch absolute (0-200psia). Additional manual valves 56, 58, 60, 62, are shown for regulatingthe pressure along the gas line, said pressure capable of beingregistered on pressure gauges 64, 66, 68, 70. The connection of the gassources can be controlled with solenoid valves 72, 74 and a pair ofcheck valves 76, 78. The output from the gaseous fuel composition sensor18 was controlled with manual valve 80 and the gaseous fuel passedthrough another check valve 82.

FIG. 4 illustrates typical results from testing of gaseous fuelcomposition sensor 18 with a plot of resistance change as a function ofgas temperature with a value of filament current set at one milliampere(1 mA). The level of filament current was set to a minimum valueconsistent with the accuracy limitations of the equipment (0.1 mvvoltmeter resolution) to minimize self heating effects. The amount ofself-heating created from filament currents of up to a few milliamperesresult in energy dissipation on the order of fractions of a microwattand thereby generate a negligible temperature change. The currentutilized for determining the temperature of gaseous flow shouldtherefore be kept below a maximum of about ten milliamperes (10 mA), andpreferably at or below a few milliamperes (2 mA–4 mA). A positiveresistance change will be exhibited for a positive change in temperaturewhen utilizing metallic materials for the filament of the thermalconductivity sensor. The relationship between temperature and resistancecan be expressed as a simplified Callendar-Van Dusen equation:R_(T)=R₀(1+αT)  (2)wherein R_(T) is the resistance in ohms at temperature T, R₀ is theresistance in ohms at T=0° C. and α is the temperature coefficient atT=0° C. in ohms/ohms/° C. R₀ and α are calculated as 30.19±0.11 Ω and(32.4±0.23)×10⁻⁴ Ω/Ω/° C. with a 95% confidence level, respectively,from the slope and intercept exhibited within FIG. 4. Utilizing Eq. 2and the associated constants, the gas temperature was measured with anaccuracy of ±1° C. without utilizing additional temperature sensors orcompensating for the small amount of current injected into the filamentof the sensor.

FIG. 5 illustrates changes in filament resistance at various injectedcurrents levels for each of the gases, specifically hydrogen H₂ andmethane CH₄. The plot of filament resistance for hydrogen gasillustrates that filament heating is less when the filament issurrounded by hydrogen gas that it is when the filament is surrounded bynatural gas. The difference in filament heating characteristics is dueto the higher thermal conductivity of hydrogen such that more heatenergy is dissipated from the filament into the surrounding hydrogen.The thermal conductivity measurements were performed at atmosphericpressure with a wall temperature of forty seven degrees Celsius (47°C.). In the low current region below ten milliamperes (10 mA), asdiscussed above, the sensor precision was not adequate to measure thegas composition, because the resistance value was largely indicative ofgas temperature. Increasing the filament current above ten milliamperes(10 mA) dramatically increased the signal levels, thereby allowingthermal conductivity to be accurately registered. It should, however, beappreciated that filament longevity is inversely related to increasedlevels of filament current. In the present embodiment, filament currentwas set for about eighty milliamperes (80 mA), which is well below thetwo hundred milliampere (200 mA) maximum current suggested by thefilament manufacturer, and which provides adequate sensitivity formixture ratio detection. The present embodiment was found to toleratesubstantial changes in the gaseous flow rate, up to and in excess of oneliter per minute, without noticeable convective filament cooling. A hightolerance to flow rate variation is preferable within the application sothat mixture ratios may be calculated without compensating for gaseousflow rate. A linear increase in sensor signal was observed within thetests as the body temperature of the sensor increased, therefore, sensorbody temperature should be measured and used for compensating the fuelcomposition measurement. Alternatively, the filament mounting block maybe held at a constant temperature with a sufficiently low gas flow rateso that the gaseous fuel mixture equilibrates at the mounting blocktemperature.

The effect of gas pressure was shown to be more complex than othergaseous mixture ratio variables. Theoretically the filament temperature,and thus the resistance of the sensor, is reduced by the amount ofgaseous thermal conduction which occurs. The amount of gaseousconduction that occurs is determined by the thermal conductivity of thegas, κ, which defines the proportionality between heat flux andtemperature gradient. Thermal conductivity is generally represented bythe kinetic theory of gases.κ=K√{square root over ((T/m)/S)}  (3)In Eq. (3) the value T1 is a proportionality constant, T is the absolutetemperature, m is the molecular mass and S is the molecularcross-section. It will be recognized that the simple kinetic formularepresented by equation Eq. (3) shows no thermal conductivity dependenceon the number density of the gas, or pressure. However, it should beappreciated that the driving parameters of the equation are mass andmolecular cross-section, and that since hydrogen, H₂, is compact and hasa low molecular weight it exhibits a high thermal conductivity which isapproximately seven times greater than that of methane CH₄. The simplekinetic model of Eq. (3) is only capable of representing thermalconductivity for “perfect” gases which exhibit meager molecular force.The limitations of the kinetic model from Eq. (3) were exhibited undervarying pressure conditions. It should be appreciated that the behaviorof hydrogen gas closely approaches the conductivity for a “perfect gas”,while the conductivity of natural gas is highly dependent on pressure.Therefore, it is preferred that gaseous fuel composition based onthermal conductivity be performed by either retaining substantiallyfixed conditions of pressure and gaseous fuel temperature, or bymeasuring gaseous temperature and pressure to be accounted for withinthe calculations for gaseous fuel composition.

FIG. 6 illustrates a three-dimensional plot of filament resistance as afunction of gaseous fuel pressure and sensor block temperature for agaseous mixture containing 80.03% methane, by mass, with the remaining19.97% comprising hydrogen.

FIG. 7 illustrates gaseous fuel composition, expressed as a methanepercentage, as a function of the gaseous pressure and measured sensorvoltage. The gaseous fuel composition was determined at a stable sensorbody temperature of 60° C. FIG. 8 is a plot of gaseous fuel compositionas a function of measured sensor voltage at three absolute temperaturevalues for the sensor body, wherein the pressure is maintained at 100psig. Gaseous fuel composition, C, may be determined from a threedimensional curve fitting algorithm, which can be developed usingmulti-variable regression analysis.C=f(P,T,E)  (4)The composition C is therefore given by the three dimensional curvefitting equation as a function of Kelvin temperature T, pressure P(psig), and sensor voltage (electromotive force in volts) E.

Utilizing the three-dimensional curve fitting algorithm, the compositionof a given fuel mixture may be determined. Fuel composition testingusing this approach yielded a worst case error level of approximately 2%(±1%), which should provide a suitable level of accuracy from which tomodulate engine combustion parameters. Although the composition of thegaseous fuel may be readily calculated from a curve fitting approach, itshould be appreciated that gaseous fuel composition may be determinedfrom any number of alternative measurement calibration techniques, curvemapping techniques, and/or equation-based compensation techniqueswithout departing from the teachings of the present invention.

FIG. 9 exemplifies an embodiment of a gaseous fuel composition sensorsystem 90 for use within an ICE so that combustion parameters may beadjusted as a function of the mixture ratio of natural gas (methane) tohydrogen. The block diagram contains a digital control circuit 92, shownas a microcontroller, that interfaces to analog current sources andsensor circuits. The sensor circuits 90 are capable of generatingmultiple current levels through sensor filament 94, which arerepresented by a high-current source 96 and a low-current source 98controlled by microcontroller 92. The voltage induced on filament 92from the application of a predetermined current level is amplified by aprogrammable gain amplifier 100 whose output is registered by ananalog-to-digital converter within microcontroller 92.

The application of low currents to filament 94 allows for thecomputation of gas temperature which can be used to compensate fuelcomposition computations. To achieve accurate temperature readings, itwill be appreciated that the low current being applied to filament 94should be insufficient to significantly elevate the filament temperatureabove the gaseous fuel temperature. The determination of gaseous fueltemperature in this manner should be performed only after the currentthrough filament 94 has been reduced and the temperature of filament 94has substantially attained thermal equilibrium with the temperature ofthe surrounding gaseous fuel mixture.

Application of higher current levels to filament 94 can sufficientlyheat the filament above the temperature of the gaseous fuel to allow thethermal conductivity of the gaseous fuel composition to be determinedunder the given set of gas temperature and pressure conditions.Switching between current levels is preferably performed by themicrocontroller which toggles between a low current value as set byinterval T1 and a high current value subject to interval T2. It will beappreciated that the dual-current sensor mode eliminates the necessityfor a separate gas temperature sensor within the circuit, while thedecreased average filament provides the additional advantage ofprolonging the service life for filament 94. The present embodiment isconfigured to adapt to a low rate of change for fuel composition,wherein the measurement intervals provide an interval of low current T1for a period of fifty seconds (50 S), alternating with an interval ofhigh current T2 for a period of ten seconds (10 S). The selected timingof filament drive current and voltage sensing provides for theregistration of the available fuel composition when the engine isstarted, and it updates that reading every minute thereafter. If aparticular application warrants more frequent fuel composition updates,faster sampling may be adopted subject to thermal equilibriumlimitations. One method of reducing the time to reach thermalequilibrium within each interval is by utilizing a filament whichexhibits a lower thermal mass. Another method would be to incorporate aseparate temperature sensor, wherein the filament may be continuouslyutilized for sensing mixture ratio.

Sensor circuit 90 provides a simple and robust method for determiningthe gaseous fuel composition so that combustion parameters may bemodulated accordingly. The dependability of sensor circuit 90 iscrucial, and it is preferable that failures and errors within any singlecomponent within the system should not prevent VGF engine operation. Itshould be appreciated that improper sensing of gaseous fuel compositioncould render the associated engine inoperable, depending on availablefuel composition, because of the large disparity between the energydensity characteristics of hydrogen and natural gas. For example,attempting to operate the engine from a hydrogen gas source usingcombustion parameters set for natural gas operation would result in aninsufficient power output along with possibly adverse spark timing, dueto the more rapid combustion of hydrogen. Therefore, the advantageswhich accrue from providing circuit redundancy should be appreciated,and may be incorporated herein without departing from the teachings ofthe present invention. By way of example, redundant sensor filaments maybe utilized, such as three filaments, that can allow the VGF engine tocontinue operating correctly despite failures or errors which occurwithin any one sensor. For example, a set of three filaments may bedriven out of phase with one another and the outputs read by themicrocontroller which is capable of executing a voting scheme toeliminate erroneous readings and to preferably generate a troubleindication upon detecting sensor readings that do not agree with oneanother. Furthermore, other elements, such as the microcontroller andother sensors also may be redundantly configured to enhancedependability.

The digital controller is exemplified as a Z180 32-bit microprocessor,from Zilog Corporation, having a 9 MHz clock, Z84C20 PIO, 128K flashmemory and a TLC2543 8 channel 12 bit A/D converter for measuring thesensor signals. An AD7302 2 channel 8 bit D/A converter from AnalogDevices Incorporated was utilized for controlling the fuel compositionoutput signal which determines the engine combustion parameters inresponse to the available mixture ratio. Software routines embeddedwithin the firmware of the microprocessor are preferably utilized forcontrolling the switching of filament current and for the calculation ofthe available gaseous fuel composition. The microprocessor preferablysolves a three-dimensional equation to determine gaseous fuelcomposition. A small routine can easily be written in the C language orother programming language for performing the composition analysisdescribed herein. VGF fuel composition may be conveniently measured bythe described use of thermal conductivity sensing, or by measuring otherdifferentiable gas characteristics. Upon determining the gaseous fuelcomposition, a fuel composition signal is communicated to an enginecontrol module (ECM) to control fuel metering, injection, and preferablythe ignition timing.

FIG. 10 represents a combustion chamber, such as within an internalcombustion engine configured for VGF operation according to the presentinvention. A cylinder 106 is shown with slidably engaged piston 108above which is a combustion chamber 110 that has a volume responsive tothe movement of piston 108 within cylinder 106. Gaseous fuel is meteredinto combustion chamber 110, filled with oxygen-containing ambient air.The gaseous fuel is introduced into the air of the combustion chamber bya fuel metering device 112, shown as an electronic fuel injector. As thepiston reaches the uppermost limit of its travel, generally referred toas “top-dead-center”, a spark is introduced by a spark plug 114 withincombustion chamber 110 to ignite the combination of gaseous fuel andoxygen which upon expansion drives piston 108 downward thus generatingmechanical power. Fuel metering device 112, and optionally the timing ofignition by spark plug 114 through ignition coil 116, are showncontrolled by electronic control module (ECM) 20. The control outputsfrom ECM 20 operate within the present invention in response to thedetected composition of the gaseous fuel from fuel source 16 which maycontain hydrogen gas, natural gas, or any mixture thereof. Prior toreceipt by the fuel metering device, gaseous fuels from fuel source 16passes through pressure regulator 14 and gaseous fuel composition sensor18. A combination of valves 118 is represented in the figure and wouldtypically comprise intake valves through which air is received prior tocombustion, and exhaust valves through which combustion by-products arelater exhausted. It will be appreciated that ECM 20 may be optionallyconfigured to control a number of additional combustion parameters, suchas the activation of intake and exhaust valves. In general, theelectronics utilized for controlling conventional engine operations aredesigned to optimize engine efficiency and reduce the level ofpollutants emitted. Consistent with these goals the ECM described foruse within the present invention incorporates a fuel composition sensorfor operation from variable gaseous fuels, while retaining theconventional incorporation of sensors to evaluate other relevant enginestate information, such as throttle setting. The ECM utilizes thecollected information, such as selecting appropriate “maps”, from whichit adjusts the operation of all the engine devices under its control. Itwill be appreciated that controlling a larger number of combustionparameters leads to increased engine efficiency and/or reduced emissionlevels. It will be further appreciated that the present invention may beimplemented on many forms of internal combustion engine, includingrotary-engines, Sterling engines, and so forth.

As can be seen, therefore, vehicles manufactured with an engine capableof operating from “variable gaseous fuels” (VGF) according to thepresent invention may be fueled from facility-based hydrogen generationfacilities and existing natural gas distribution facilities. Variablegaseous fuels as described herein comprise either hydrogen gas, naturalgas, or any arbitrary mixture of the two gases. VGF operation isparticularly attractive for use within hybrid combustion/electricvehicles.

The present invention provides an engine which automatically“self-adapts” to arbitrary percentages of hydrogen in the gas mixture,wherein a single gaseous fuel reservoir can be used to contain this“variable gaseous fuel” which may contain a mixture of whatever naturalgas or hydrogen gas fuel was available at refueling. The heat value,flame velocity, and transport properties of the combusted gaseous fuelcan vary by nearly an order of magnitude depending on the proportion ofhydrogen gas and natural gas being utilized. Thus, substantial changesto the combustion variables are required to achieve efficient operationfrom a mixed composition fuel.

Operation of an ICE from multiple admixed gases presumes that thecombination results in a substantially stable mixture that is not proneto reaction or separation within the gaseous fuel reservoir. Hydrogengas does not react with components of natural gas and mixtures of thetwo gases provide a stable composition. To achieve smooth operation fromany variable gaseous fuel it is preferred that the fuel be uniformlyblended so that the combustion process need not rapidly adapt to thespurious receipt of un-mixed quantities of the fuel gases. It should beappreciated that the typical methods of filling a gaseous fuel tank froma high pressure gaseous source introduces turbulence within the fueltank due to inrushing gas that should initiate rapid mixing. However,even if the two gaseous components are brought together without initialmixing, it should be appreciated that the diffusion time constant forthe gases is short and thereby a uniform mixture is rapidly attained.The time constant for diffusion may be readily determined from a simpledimensional analysis (or by use of the diffusion equation) whichsuggests a time constant on the order of L²/D₁₂, where L is anappropriate internal dimension of the containing vessel and D₁₂ is thebinary diffusion coefficient. For hydrogen-methane, D₁₂=0.72 cm²/sec at298° K. Thus the diffusion mixing times are on the order of 1000 secondsfor a 30 cm vessel. This suggests that even in the case of very slownon-turbulent filling of the tank, such as slow overnight filling, thegas will tend to rapidly reach uniformity. Furthermore, the gases arenot subject to separation except at temperatures substantially belowenvironmental ambient conditions, such as when the methane gas condensesto a liquid and the hydrogen remains in a gaseous form. It should alsobe readily appreciated that at typical ambient conditions, the gaseouscombination would not be subject to separation due to the effects ofgravity. At typical ambient temperatures, density changes caused bygravity may be accurately represented by an exponential relationshiphaving a scale height proportional to kT/mg, where k is the Boltzman'sconstant, m the molecular mass, and g the gravitational constant. Forair, the scale height is about 10 km, for methane 14.5 km, and forhydrogen near 100,000 meters. Hence the gravity effect on density isless than one part per thousand at normal temperatures. Finally, itshould also be appreciated that the VGF engine is preferably configuredfor continuous adaptation to the available gaseous fuel composition fromthe gas fuel source, wherein minor non-uniformities in the gascomposition may be compensated for.

Accordingly, it will be seen that this invention provides an apparatusand method for operating internal combustion engines on any arbitrarymixture of hydrogen and natural gas. The present invention includesmeans for sensing gaseous fuel composition and controlling theparameters of combustion, such as fuel metering and ignition timing,wherein the engine can attain high operating efficiencies from anymixture of gaseous fuel which largely comprises hydrogen gas, naturalgas, or any combination thereof, along with any of various additives orimpurities. While a thermal conductivity sensor is preferably used as ameans for determining the available gaseous fuel composition so that thecombustion parameters of the engine may be properly modulated, theinvention contemplates other means of characterizing the fuel mixtureusing one or more alternative measurements that register adifferentiable characteristic of the subject gases. Furthermore, whilemodulation of combustion parameters preferably comprises changing theamount of fuel being metered to the engine and optionally the ignitiontiming, and/or valve timing, to optimize engine operating efficiency, itwill be appreciated that a number of additional engine operatingparameters may be adjusted in response to changes in the composition ofthe gaseous fuels without departing from the present invention.

It will be readily appreciated that the availability of vehicles whosefuel storage tanks may be filled with quantities of either natural gasor hydrogen would greatly simplify the infrastructure problemsassociated with adopting renewable hydrogen as a new fuel source.Vehicles which incorporate VGF engines can utilize either form of gas,wherein the driver may select a type of gaseous fuel to be used inresponse to factors such as availability and/or cost. In general, theuse of natural gas by itself provides maximum range and power due to itsinherently higher energy density, while the use of hydrogen gas byitself provides substantially lowered emissions and eventually a loweredcost factor. The range, power, cost, and emissions available fromblending the two gaseous fuels being dependent on the specific mixtureratio being combusted. It will be further appreciated that uponequipping vehicles with VGF engines, fuel distributors may elect to selleither, or both, forms of gaseous fuel. These fuels could be distributedseparately or in any desired mixture ratio. Furthermore, gas refuelingequipment at fuel distribution facilities could be configured with gascomposition sensors, such as a thermal conductivity sensor according todescribed aspects of the present invention, whereby hydrogen gas andnatural gas may be dispensed in combination to achieve a user specifiedmixture ratio within their fuel tank according to desired performanceand cost factors.

Utilizing a vehicle equipped for operation from variable gaseous fuelsthereby provides the flexibility to operate from home-generated hydrogengas supplies or any available mixture of hydrogen gas and natural gasthat is available from a fueling station. Utilizing the teachings of thepresent invention, therefore, can provide for creating VGF engines thatprovide a smooth fuel migration path for both vehicle manufacturers andfuel distributors from a high-emission non-renewable fossil fuel sourceto a clean renewable fuel source.

A number of advantages also accrue from manufacturing vehicles capableof VGF operation. A migration path is provided with VGF technology fromthe current use of less costly hydrocarbon fuels, to a renewable sourceof energy that can be generated domestically. Any ICE having at leastone combustion chamber that is capable of burning gaseous fuels may beconfigured to operate on a variable gaseous range of fuels according tothe present invention, and can he produced at a modest cost premium overpresent day non-VGF operable engines. A VGF engine operating on purehydrogen, and configured with exhaust gas recirculation and catalyticscrubbing to remove the remaining NO_(x), should be capable of meetingthe criterion imposed by zero emission standards.

Note also that the ability to perform home refueling, such as by using a“personal fueling appliance” (PFA), can provide a low-cost homerefueling capability similar to the charging of an electric car. Incontrast to an electric vehicle, however, the range of a VGF equippedvehicle can be extended indefinitely with natural gas that is currentlyavailable at many vehicle refueling stations. One proposed PFA isdesigned in a form factor that approximates the size of a clothes-washerand requires only a supply of water and electricity to generate a 300bar (over 4000 psig) source of hydrogen. Natural gas refueling isavailable internationally and provides a base level of infrastructurefor the distribution of gaseous fuels upon which hydrogen distributionmay be built. VGF engines being capable of operating from any mixture ofavailable hydrogen and natural gas are ideally suited for utilizinggases generated from land-fill or digesters due to an inherentinsensitivity to impurities. It should be appreciated that generated gasfuel sources typically contain levels of impurities which may damage orotherwise hinder proper fuel cell operation. Internal combustion enginesadapted with sensors and combustion controls to achieve VGF operationprovide a bridge between current non-renewable energy sources andenvironmentally friendly renewable energy sources. Sales of VGF equippedvehicles would stimulate the further development of a renewable hydrogenenergy refueling infrastructure that could eventually support additionaltechnologies, such as vehicles powered from hydrogen fuel cells whenthat technology matures. The early introduction of hydrogen for fuelingVGF vehicles would provide an impetus for establishing a hydrogeninfrastructure that includes both physical facilities and the adoptionof new fueling codes and regulations.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodimentsof this invention. Therefore, it will be appreciated that the scope ofthe present invention fully encompasses other embodiments which maybecome obvious to those skilled in the art, and that the scope of thepresent invention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” All structural, chemical, and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe present claims. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the presentinvention, for it to be encompassed by the present claims. Furthermore,no element, component, or method step in the present disclosure isintended to be dedicated to the public regardless of whether theelement, component, or method step is explicitly recited in the claims.No claim element herein is to be construed under the provisions of 35U.S.C. 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for.”

1. A variable gaseous fuels engine, comprising: an internal combustionengine having a combustion chamber; said combustion chamber adapted toreceive a mixture of a first gaseous fuel and a second gaseous fuel forcombustion therein; means for detecting the ratio of said first andsecond gaseous fuels in said mixture and generating a fuel compositionsignal in response to said detected ratio; and an engine control module;said engine control module adapted to modulate the quantity of saidgaseous fuel mixture received within said combustion chamber in responseto said fuel composition signal; wherein said engine is thereby capableof operating from any arbitrary mixture of said first and second gaseousfuels.
 2. A variable gaseous fuels engine as recited in claim 1, whereinsaid gaseous fuel composition detecting means comprises: an electronicsensor; said electronic sensor adapted to differentiate one or morecharacteristics of hydrogen from one or more characteristics of naturalgas.
 3. A variable gaseous fuels engine as recited in claim 2, whereinsaid electronic sensor comprises a thermal conductivity sensor.
 4. Avariable gaseous fuels engine as recited in claim 3, wherein saidthermal conductivity sensor comprises: a housing having a passagewaythrough which said gaseous fuel can flow; and a thermal conductivitysensor element positioned within said passageway; said thermalconductivity sensor clement adapted to make fluidic contact with saidgaseous fuel.
 5. A variable gaseous fuels engine as recited in claim 4,wherein said housing is maintained at a substantially constanttemperature.
 6. A variable gaseous fuels engine as recited in claim 4,wherein said thermal conductivity sensor element comprises a filamentthrough which a first electrical current is passed for the registrationof thermal conductivity for said gaseous fuel with which it is incontact.
 7. A variable gaseous fuels engine as recited in claim 5:wherein said first electrical current is of sufficient amperage to heatsaid filament to a temperature exceeding the temperature of said gaseousfuel; and wherein the thermal conductivity of said gaseous fuel isdetermined from analyzing the conductive heat dissipation which occursto moderate the elevation of filament temperature.
 8. A variable gaseousfuels engine as recited in claim 7, wherein said first electricalcurrent is in excess of one milliampere.
 9. A variable gaseous fuelsengine as recited in claim 7, wherein said first electrical current isless than approximately two hundred milliamperes.
 10. A variable gaseousfuels engine as recited in claim 7: wherein the amount of said filamentheating is detected by registering electrical resistance of saidfilament; said resistance comprising the quotient of filament voltagedivided by said first current induced in said filament.
 11. A variablegaseous fuels engine as recited in claim 10, wherein conductivity of thegaseous mixture is determined from the amount of filament temperaturemoderation which occurs in response to conductive energy losses.
 12. Avariable gaseous fuels engine as recited in claim 6, wherein saidfilament comprises a metallic material.
 13. A variable gaseous fuelsengine as recited in claim 12, wherein said metallic materialsubstantially comprises tungsten.
 14. A variable gaseous fuels engine asrecited in claim 13, wherein said filament contains an operable quantityof Rhenium.
 15. A variable gaseous fuels engine as recited in claim 14,wherein said quantity of said Rhenium is up to approximately tenpercent.
 16. A variable gaseous fuels engine as recited in claim 14,wherein said quantity of Rhenium is greater than approximately twopercent.
 17. A variable gaseous fuels engine as recited in claim 4,wherein said filament is positioned in a chamber that is in fluidcommunication with said passageway.
 18. A variable gaseous fuels engineas recited in claim 17, wherein said filament is positioned within saidchamber a predetermined offset distance from the center of saidpassageway.
 19. A variable gaseous fuels engine as recited in claim 18,wherein said predetermined offset distance is in relation to thediameter of said chamber.
 20. A variable gaseous fuels engine as recitedin claim 19, wherein said offset distance is given by a distanceapproximately equivalent to four times the diameter of said chamber. 21.A variable gaseous fuels engine as recited in claim 18: wherein thediameter of said chamber is approximately one-half centimeter; andwherein the distance from the center of said passageway to said filamentis approximately 2.3 centimeters.
 22. A variable gaseous fuels engine asrecited in claim 1, further comprising: a pressure regulator; saidpressure regulator adapted to regulate pressure of said gaseous fuelflowing to said combustion chamber.
 23. A variable gaseous fuels engineas recited in claim 22: wherein said pressure regulator is adapted toreduce the gaseous fuel pressure to a predetermined value; and whereinthe predetermined value of fuel pressure is consistent with propermodulation of gaseous fuel quantity by said engine control module.
 24. Avariable gaseous fuels engine as recited in claim 23, wherein saidpredetermined value is approximately one hundred forty-five pounds persquare inch.
 25. A variable gaseous fuels engine as recited in claim 4,further comprising means for registering the temperature of said gaseousfuel whose conductivity is being registered by said thermal conductivitysensor.
 26. A variable gaseous fuels engine as recited in claim 25:wherein the temperature of said gaseous fuel is measured by passing asecond current through said filament; wherein said second current issubstantially less than said first current; and wherein the voltageexpressed across said filament by said second current is substantiallyindicative of the temperature of said filament in substantial thermalequilibrium with said surrounding gaseous fuel.
 27. A variable gaseousfuels engine as recited in claim 26, wherein said second current is lessthan approximately ten milliamperes.
 28. A variable gaseous fuels engineas recited in claim 27, wherein said second current is approximately onemilliampere.
 29. A variable gaseous fuels engine as recited in claim 1,wherein said engine control module is adapted to control ignition timingwithin said combustion chamber in response to said fuel compositionsignal.
 30. A variable gaseous fuels engine as recited in claim 1:wherein said engine control module is adapted for scaling the amount offuel being metered to said combustion chamber under current operatingconditions; wherein the scaling of the fuel amount to said combustionchamber is based on an estimation of the energy density contained insaid gaseous fuel mixture; and wherein the composition of said gaseousfuel mixture has been communicated by the receipt of said fuelcomposition signal.
 31. A variable gaseous fuels engine capable ofoperating from a variable mixture of hydrogen gas and natural gas,comprising: an internal combustion engine having a combustion chamber;said combustion chamber adapted to receive a mixture of a first gaseousfuel and a second gaseous fuel for combustion therein; a thermalconductivity sensor; said thermal conductivity sensor adapted togenerate a fuel composition signal indicative of the ratio of said firstand second gaseous fuels in said mixture; and an engine control module;said engine control module adapted to modulate said quantity of saidgaseous fuel mixture received within said combustion chamber in responseto said fuel composition signal; wherein said engine is thereby capableof operating from any arbitrary mixture of said first and second gaseousfuels.
 32. A variable gaseous fuels engine as recited in claim 31,wherein said engine control module is adapted to modulate ignitiontiming in response to changes in gaseous fuel composition as indicatedby said fuel composition signal.
 33. A variable gaseous fuels engine asrecited in claim 31, wherein said thermal conductivity sensor comprises:a housing having a passageway through which gaseous fuel can flow; and athermal conductivity sensor element positioned within said passageway.34. A variable gaseous fuels engine as recited in claim 33, wherein saidhousing is maintained at a controlled temperature.
 35. A variablegaseous fuels engine as recited in claim 33: wherein said thermalconductivity sensor element comprises an electrical filament; andwherein a first electrical current is passed through the filament forsensing the thermal conductivity of said gaseous fuels in contacttherewith.
 36. A variable gaseous fuels engine as recited in claim 35:wherein said first electrical current is of sufficient amperage to heatsaid filament to a temperature which is elevated above that of saidgaseous fuel mixture; whereby the thermal conductivity of said gaseousfuel mixture is determined.
 37. A variable gaseous fuels engine asrecited in claim 36, wherein said first electrical current exceedsapproximately one milliampere.
 38. A variable gaseous fuels engine asrecited in claim 36, wherein said first electrical current is underapproximately two hundred milliamperes.
 39. A variable gaseous fuelsengine as recited in claim 36: wherein conductivity of said gaseousmixture is determined from the amount of filament temperature elevationwhich occurs; wherein said filament temperature elevation is determinedfrom the resistance of said filament as given by quotient which resultsfrom dividing filament voltage by said first filament current.
 40. Avariable gaseous fuels engine as recited in claim 35, wherein saidfilament comprises a metallic material.
 41. A variable gaseous fuelsengine as recited in claim 40, wherein said metallic materialsubstantially comprises Tungsten.
 42. A variable gaseous fuels engine asrecited in claim 40, wherein said filament comprises less thanapproximately ten percent Rhenium.
 43. A variable gaseous fuels engineas recited in claim 40, wherein said filament comprises greater thanapproximately two percent Rhenium.
 44. A variable gaseous fuels engineas recited in claim 35: wherein said filament is positioned within achamber fluidly connected to said passageway; and wherein said chamberis adapted to partially isolate said filament from changes in convectivecooling that may occur in response to variations in the gaseous fuelflow rate.
 45. A variable gaseous fuels engine as recited in claim 31,further comprising: a pressure regulator; said pressure regulatoradapted to regulate pressure of said gaseous fuel flowing to saidcombustion chamber.
 46. A variable gaseous fuels engine as recited inclaim 45, wherein said pressure regulator is adapted to limits thepressure enroute to said combustion chamber to a predetermined maximumvalue.
 47. A variable gaseous fuels engine as recited in claim 46,wherein said maximum value of pressure is approximately one hundredforty five pounds per square inch.
 48. A variable gaseous fuels engineas recited in claim 31, further comprising means for detecting thetemperature of the gaseous fuel whose thermal conductivity is to beregistered by said thermal conductivity sensor.
 49. A variable gaseousfuels engine as recited in claim 48: wherein the temperature of saidgaseous fuel is measured by passing a second current through saidfilament within said thermal conductivity sensor; wherein said secondcurrent is substantially less than said first current; and wherein thevoltage induced in the filament by said second current is substantiallyindicative of the temperature of the filament in substantial thermalequilibrium with the surrounding gaseous fuel.
 50. A variable gaseousfuels engine as recited in claim 49, wherein said second current is lessthan approximately ten milliamperes.
 51. A variable gaseous fuels engineas recited in claim 50, wherein said second current is approximately onemilliampere.
 52. A variable gaseous fuels engine as recited in claim 31,wherein said engine control module is adapted to vary ignition timing ofsaid internal combustion engine in response to the determined fuelcomposition.
 53. A variable gaseous fuels engine as recited in claim 31:wherein said engine control module is adapted to modulate the amount offuel being metered to said combustion chamber; and wherein fuel meteringis based on an estimation of the energy density contained in saidgaseous fuel mixture whose composition has been determined.
 54. In aninternal combustion engine configured for generating mechanical energyby the combustion of a gaseous fuel mixture of first and second gaseousfuels, the improvement comprising: a fuel composition sensor positionedfor contacting said gaseous fuel mixture; said fuel composition sensoradapted to generate a gaseous fuel composition signal indicative of theratio of said first and second gaseous fuels in said gaseous fuelmixture; and an engine control module; said engine control moduleadapted to modulate said quantity of said gaseous fuel received withinsaid combustion chamber in response to said fuel composition signal;wherein said engine is thereby capable of operating from any arbitrarymixture of said first and second gaseous fuels.
 55. An improved internalcombustion engine as recited in claim 54, wherein the gaseous fuelcomposition substantially comprises hydrogen gas, or natural gas, or anycombined mixture of hydrogen and natural gas.
 56. An improved internalcombustion engine as recited in claim 54: wherein said fuel compositionsensor comprises a sensor capable of registering a differentiablecharacteristic of the admixed constituents of said gaseous fuel; andwherein said differentiable characteristic is substantially indicativeof fuel composition.
 57. An improved internal combustion engine asrecited in claim 56, wherein said differentiable characteristic isregistered by a thermal conductivity sensor positioned for contact withsaid gaseous fuel.
 58. An improved internal combustion engine as recitedin claim 57: wherein said thermal conductivity sensor comprises a heatedfilament retained in contact with said gaseous fuel; and wherein thetemperature of said heated filament in relation to the temperature ofsaid gaseous fuel is utilized as an indicator of the thermalconductivity of said gaseous fuel which is in contact with said heatedfilament.
 59. A fuel composition sensor capable of communicating adifferentiable characteristic between at least two gaseous fuels withina gaseous fuel mixture, said characteristic being communicated forreceipt by an electronic engine control module within an internalcombustion engine that operates subject to the receipt of variablemixtures of gaseous fuel, comprising: a housing having a passagewaythrough which a gaseous fuel mixture passes prior to receipt by theinternal combustion engine; a filament positioned within said passagewayand positioned to establish fluidic contact with said gaseous fuelmixture; a first electrical current source capable of being connected tosaid filament; said first electrical current source capable of inducingsufficient current flow within said filament to increase the temperatureof said filament above the temperature of the surrounding gaseous fuelcomposition; and voltage measurement means configured to registerfilament voltage and to communicate said filament voltage to anelectronic engine control module; whereby the ratio of a first gaseousfuel and a second gaseous fuel in said gaseous fuel mixture isdetermined by evaluating the thermal conductivity of said gaseous fuelmixture as a function of filament voltage; wherein said fuel compositionsensor renders said engine capable of operating from any arbitrarymixture of said first and second gaseous fuels.
 60. A fuel compositionsensor as recited in claim 59, wherein the gaseous fuel comprises avariable gaseous mixture of fuels comprising a first gaseous fuel, or asecond gaseous fuel, or an admixed combination of said first gaseousfuel and said second gaseous fuel.
 61. A fuel composition sensor asrecited in claim 60, wherein said first gaseous fuel comprises hydrogengas.
 62. A fuel composition sensor as recited in claim 60, wherein saidsecond gaseous fuel comprises natural gas.
 63. A fuel composition sensoras recited in claim 59, wherein said housing is maintained at asubstantially fixed temperature.
 64. A fuel composition sensor asrecited in claim 59, wherein said first electrical current source iscapable of inducing a current in excess of approximately one milliamperewithin said filament.
 65. A fuel composition sensor as recited in claim59, wherein said first electrical current source is capable of inducinga current less than or equal to approximately two hundred milliampereswithin said filament.
 66. A fuel composition sensor as recited in claim59, wherein said filament comprises a metallic material.
 67. A fuelcomposition sensor as recited in claim 66, wherein said metallicmaterial substantially comprises Tungsten.
 68. A fuel composition sensoras recited in claim 67, wherein said Tungsten comprises less thanapproximately ten percent by weight of Rhenium.
 69. A fuel compositionsensor as recited in claim 67, wherein said Tungsten comprises at leastapproximately two percent by weight of Rhenium.
 70. A fuel compositionsensor as recited in claim 59, wherein said filament is positionedwithin a chamber of said passageway to isolate said filament from theconvective influence of said gaseous fuel flow through said passageway.71. A fuel composition sensor as recited in claim 70, wherein saidfilament is offset from the center of said passageway by a distanceapproximately equivalent to four times the diameter of said chamber. 72.A fuel composition sensor as recited in claim 71, wherein the diameterof said chamber is approximately one half centimeter and the distancefrom the center of the passageway to said filament is approximately twocentimeters.
 73. A fuel composition sensor as recited in claim 59,further comprising means for registering the temperature of the gaseousfuel surrounding said filament and communicating a signal in response tosaid temperature for receipt by an electronic engine control module. 74.A fuel composition sensor as recited in claim 73: wherein saidtemperature registration means comprises a second electrical currentsource which is incapable of generating sufficient current to causesubstantial filament heating; and wherein gaseous fuel temperature canbe determined from the registered filament voltage.
 75. A fuelcomposition sensor as recited in claim 74, wherein said second currentis less than approximately ten milliamperes.
 76. A fuel compositionsensor as recited in claim 75, wherein said second current isapproximately one milliampere.
 77. A method of operating an internalcombustion engine from a variable mixture of gaseous fuels, comprising:determining the ratio of a first gaseous fuel and a second gaseous fuelin said mixture; determining an amount of said gaseous fuel mixture tobe metered into said internal combustion engine based on said ratio; andadjusting fuel metering of said gaseous fuel mixture into said internalcombustion engine based on said ratio; wherein said engine is therebycapable of operating from any arbitrary mixture of first and secondgaseous fuels.
 78. A method as recited in claim 77, wherein said gaseousfuel comprises a first gaseous fuel, or a second gaseous fuel, or anyadmixed combination of said first and said second gaseous fuels.
 79. Amethod as recited in claim 78, wherein said first gaseous fuel compriseshydrogen gas.
 80. A method as recited in claim 78, wherein said secondgaseous fuel comprises natural gas.
 81. A method as recited in claim 78,wherein detecting the composition of the gaseous fuel mixture containingsaid first and said second gaseous fuel comprises finding the mixtureratio of said first gaseous fuel within said second gaseous fuel.
 82. Amethod as recited in claim 78, wherein the detection of the gaseous fuelcomposition comprises: detecting the thermal conductivity of saidgaseous fuel being received by said internal combustion engine; andevaluating the relative thermal conductivity contributions of eachprimary constituent of said gaseous fuel mixture to arrive at a gaseousfuel composition value expressed as a percentage of said first gaseousfuel within said second gaseous fuel.
 83. A method as recited in claim82, wherein detecting thermal conductivity is comprising: supplying anamount of energy to heat a filament that is retained in contact withsaid gaseous fuel to a temperature which exceeds the gaseous fuel;determining the temperature of the heated filament; and determiningthermal conductivity from evaluating filament temperature in relation tothe supplied energy.
 84. A method as recited in claim 83, whereinsupplying the energy to heat the filament comprises inducing apredetermined current to flow through the filament.
 85. A method asrecited in claim 84, wherein determining the temperature of the filamentcomprises: detecting the voltage which exists across said filament;computing filament resistance from ohm's law, R=V/I; and finding thecharacteristic filament temperature from the computed filament Lance,wherein empirical filament data is used for correlating filamentresistance to filament temperature.
 86. A method as recited in claim 77,further comprising maintaining gaseous fuel pressure at a substantiallyconstant pressure, whereby the conditions are simplified under whichfuel composition is detected.
 87. A method as recited in claim 77,further comprising maintaining gaseous fuel temperature at asubstantially constant temperature, whereby the conditions aresimplified under which the fuel composition is detected.
 88. A method asrecited in claim 77, further comprising measuring said gaseous fueltemperature to increase the accuracy of detecting the composition ofsaid gaseous fuel.